1. The Field of the Invention
Embodiments of the present invention relate to interfaces between optical transceivers and computers or communications devices that operate with the transceivers. More particularly, exemplary embodiments of the present invention relate to an electrical pad architecture that permits interoperability between optical transceiver modules and computers or communications devices.
2. The Relevant Technology
In the field of data transmission, one method of efficiently transporting data is through the use of fiber optics. Typically, data transmission via fiber optics is implemented by way of an optical transmitter, such as a light emitting diode or laser, while data reception is generally implemented by way of an optical receiver, such as a photodiode. Light signals allow for extremely high transmission rates and very high bandwidth capabilities. Also, light signals are resistant to electro-magnetic interferences that would otherwise interfere with electrical signals. Light signals are more secure because they do not allow portions of the signal to escape from the fiber optic cable as can occur with electrical signals in wire-based systems. Light also can be conducted over greater distances without the signal loss typically associated with electrical signals on copper wire.
As with copper wire or other conductors, optical cables allow for the bi-directional flow of data. One method of achieving bi-directional communication is through the use of two fiber optic cables. A first cable can be used to transmit data from a first communications device to a second communications device and the second cable can be used for transmitting data from the second communications device to the first communications device. Such a configuration is depicted in FIG. 1, which depicts a standard small form factor pluggable (SFP) connector configuration 100.
Connector configuration 100 includes a first communications module 102 and a second communications module 104 connected by a first cable 106 and a second cable 108. A transmitter 110 in first communications module 102 is connected via first cable 106 to a receiver 112 in second communications module 104. Similarly, a transmitter 114 in second communications module 104 is connected via a second cable 108 to a receiver 116 in first communications module 102. Thus, data is transmitted between first communications module 102 and second communications module 104 unidirectionally on each of cables 106, 108 from transceivers 110, 114 to receivers 112, 116, respectively.
Nevertheless, it is often desirable to limit the number of fiber optic cables between two communication points to save on material costs and installation. The link density is also limited by the number of fiber optic connectors that can be fitted on the face plate of a switch box containing an array of transceivers. This need has led to the development of bi-directional systems that limit the number of cables (and connectors) by both sending and receiving data on the same fiber optic cable. This is possible because of the directional nature of an optical signal propagating along a fiber optic cable. Generally, the use of circulators or beam splitters makes bi-directional communication possible on a single fiber optic cable.
A conventional bi-directional transceiver module configuration 200 is depicted in FIG. 2. This method of bi-directional communication along a single fiber-optic cable involves the use of lasers with different wavelengths. Commonly, a 1550 nanometer distributed feedback (DFB) laser is used to propagate an optical signal in one direction, while a 1310 nanometer Fabry Perot laser (FP) is used to propagate the optical signal in the opposite direction. This configuration has some drawbacks. The configuration requires two types of complementary transceivers, with different transceivers being used at the two communications devices engaging in the bi-directional communication. For example, one communications device must have a transceiver with a 1550 nanometer transmitter and a 1310 nanometer receiver, while the other communications devices must have a complementary transceiver having a 1310 nanometer transmitter and a 1550 nanometer receiver.
This bi-directional configuration 200 allows bi-directional data transmission between a first module 202 and a second module 204 via a single cable 206. In this configuration, each of the first and second modules 202, 204 has a transmitter 208, 210, respectively, for transmitting at a distinct wavelength from the other. Consequently, first module 202 transmits at a first wavelength (e.g. 1550 nanometers) and second module 204 transmits at a second wavelength (e.g. 1310 nanometers). Similarly, first module 202 has a first receiver 212 for receiving signals propagated at the second wavelength. Second module 204 has a second receiver 214 for receiving signals propagated at the first wavelength. First and second modules 202, 204 as depicted, also contain beam splitters 216, 218, respectively. Beam splitters 216, 218 separate incoming signals propagated at one wavelength from outgoing signals propagated at a different wavelength. The first and second modules 202, 204 are structurally distinct. They must be carefully paired so that each can receive the proper signal transmitted by the opposing module. However, industry standards are changing.
The telecommunications industry has a continuous need to both increase data transmission rates and to migrate from larger to smaller devices without sacrificing data transmission rates. For example, gigabit interface connectors (GBIC) are being replaced by small form factor connectors, often small form factor pluggable (SFP) connectors. GBIC converters include an interface module that converts the light signal from a fiber channel cable into electronic signals for use by a network interface card. SFP connectors provide the same functionality as a regular GBIC connector but in a smaller and denser physical size. Nevertheless, because of the large volume of legacy cable and connector systems that are already in use, the need for smaller and faster systems is tempered by the desire to avoid replacing existing cables and other legacy devices.
One recent approach utilizes existing Lucent Connector (LC) cables. These LC cables have paired fibers, each of which conventionally transmits optical data unidirectionally. This approach uses each cable for bi-directional data transmission and does not require two types of modules since both transceivers in the module are identical. This transceiver module requires a total of four lasers and four photodetectors, or one for each of two distinct wavelengths that are transmitted in opposite directions in each of the two cables. The modules require a complex negotiation procedure by which opposing transceiver modules at either end of an optical cable communicate to determine the wavelengths that each will send and each will receive.
Another bi-directional approach to increasing data transmission capacity on existing dual cable systems is to transmit signals in opposing directions along a single wavelength on each optical cable, thus requiring only one transmitter and one receiver at each end of each optical cable. However, the use of identical wavelengths results in a problematic optical reflection that can be caused by the fiber interconnects. A receiver sees the data transmissions from the transmitters at both ends of the optical cable rather than just the intended transmitter at the opposite end of the optical cable. This system therefore requires the use of complex echo cancellation devices to remove the reflected data transmissions that are not intended to reach the receiver.
As noted above, various optical transceiver modules for communicating bi-directional signals on optical fibers have been developed. These transceiver modules can use optical fiber infrastructures more efficiently and can provide a higher transceiver density in the chassis or patch panel receiving the transceivers. However, it is often difficult for network administrators to adopt such bi-directional optical transceiver modules because of the existing and expensive communications devices that are configured for use with unidirectional transceivers.
For example, the Small Form-Factor Pluggable Transceiver Multi-Source Agreement (SFP MSA), which is incorporated herein by reference, specifies a specific pad architecture. Pads are electrical contacts generally formed on a flat surface that electrically connect a module, such as a transceiver module, to a patch panel or other device. The pads are a male portion of a connector, while the corresponding female portion is found in the patch panel. In some applications, the pads are found on both a top surface and a bottom surface of a portion of an optoelectronic module. The SFP MSA defines specific uses for the pads. However, the SFP MSA was not created to support small form factor pluggable optical transceiver modules that use bi-directional communication. Thus, the use of bi-directional transceivers generally has required the acquisition of communications devices that can electrically interface with the bi-directional transceiver modules to receive and transmit data. This has resulted in the abandonment of otherwise state-of-the-art communications devices that operate according to, for example, the SFP MSA.